1. Field of the Invention
The invention relates to a fan, in particular a fan for radiators of internal-combustion engines in motor vehicles.
2. Description of Related Art
A conventional fan having inner radial blades and nouter semi-axial blades is disclosed in Swiss Patent 63 202. The entirety of a conical hub supporting the axial blades is designed as a centrifugal fan or radial blower. An object of the Swiss patent was to provide an axial fan without a so-called center cup, i.e. a hub through which axial flow can occur. Because a recirculation flow forms in such a hub, the inner region of this known axial fan incorporates the radial blower. In the Swiss patent, the leading edges of the radial and axial blades are flush with one another. At the outflow region of the radial blower, an outlet parallel to the axis of rotation is provided by a deflection in the blade passages. The fan disclosed in the Swiss patent is driven directly via a shaft fastened to the centrifugal fan.
German Patent 94 03 217 discloses an axial fan having inner and outer axial blades separated by a coaxially running intermediate ring. The spacing between the outer axial blades is substantially smaller, or the blade number is correspondingly greater, than that of the inner axial blades. According to the German patent, an increased fan output is achieved.
One consequence of installing fans in motor vehicles behind the radiator of the internal-combustion engine and in front of the internal-combustion engine is that the fan, which is in principle designed as an axial fan, is subjected to relatively pronounced throttling. This produces a semi-axial flow as described in detail in the Behr company brochure entitled "Dusenmantellufter fur Nutzfahrzeugkuhlanlagen" by Kurt Hauser, published in MTZ, Motortechnische Zeitschrift, Volume 53, No. 11/92.